AW: Ground temperature

["hotline" <hotline@xxxxxxxxxxxxxx>]

Dear Helmi Ben Rejeb

As you can see in the PREBID help
for boundary walls a external convection coefficient lower then 0.001 means direct contact.
In this case the external convection coefficient is ignored and the Boundary temperature is 
set directly to the outside surface temperature.
 
More physically correct is a high external convection coefficient for a good contact e.g 999
In this case the outside surface temperature is close but not exact equal to the boundary temperature.
 
Note for other wall types then BOUNDARY you have to enter high number for the external convection coefficient 
for very good contact.
 
 

 
 
 
The modelling of the ground influence is quite complex. Depending on the dimensions of the building and the insulation towards the ground.
A Simple approximation is the earth temperature profile TYPE 164  available as a nostandard TYPE or in the geothermal TESS Library.
More detailed is the real modelling of the whole ground for several years with a seasonal thermal storage model like the nostandard type 142.
 
best regards
Mit sonnigen Grüßen, 

Ihr TRNSYS Hotline Team 

T.Welfonder, M.Rudolph 


Mailto:Hotline@transsolar.com; http://www.transsolar.com 
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 -----Ursprüngliche Nachricht-----
Von: helmi [mailto:helmi_rjb@yahoo.fr] 
Gesendet: Sonntag, 1. Juni 2003 15:08
An: trnsys group
Betreff: Ground temperature



Dear Trnsys users

What is the value we must take for the external convection coefficient of the floor, while we are describing a building in the Prebid?

And how to model the influence of the ground temperature?

Note that in the Trnsys examples, the value of Hback was very low, and the ground temperature was fixed.

Thank you in advance.

Best regards.



Ing. Helmi Ben Rejeb
Ecole Nationale d'Ingénieurs de Tunis, BP 37, Le belvédère, 1002 Tunis, Tunisia. 



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